2. A 9-year-old boy presents to the ED with his mother with puffy eyes and scant urine. His general health has been good until 2 weeks ago when he developed a sore throat and swollen glands. An antibiotic was started at that time. He appears well except for facial swelling and edema in his feet. Blood pressure is 150/90 mm Hg. The remainder of the physical examination is normal. Laboratory testing reveals a serum creatinine level of 1.8 mg/dL, BUN of
35 mg/dL, albumin level of 3.2 g/dL (normal, 3.3-5.2 g/dL), serum complement C3 level of 80 mg/dL (normal, 100-233 mg/dL), serum complement C4 level of 25 mg/dL (normal, 14-18 mg/dL), anti-streptolysin O titer of 230 U (normal, < 200 U), and an antinuclear antibody titer of 1:20 (> 1:40 is abnormal). Urinalysis reveals 1+ protein, 10 to 20 red blood cells, 2 to 6 white blood cells, and occasional red blood cell casts. Urine protein is 2 g/24 hr. What is the next step in the management of this patient?

3. A 60-year-old man presents to the ED with a 6-week history of fatigue, myalgias, weight loss, and shortness of breath. Past medical history is significant for hypertension for 10 years. Urine output and blood pressure are normal. There is no skin rash, hepatomegaly, splenomegaly, or peripheral edema. Laboratory testing reveals a hemoglobin level of 10 g/dL (normal, 13-18 g/dL), BUN of 68 mg/dL, and serum creatinine level of 4.5 mg/dL. Serum electrolytes are normal. Serum creatinine 1 year ago was 0.9 mg/dL. Urinalysis shows 2+ protein, 15 to 20 red blood cells, 5 to 10 white blood cells, and a few erythrocyte casts and granular casts per high-power field. Complement levels are normal. Ultrasound of the kidneys reveals 11-cm kidneys bilaterally with no hydronephrosis. Chest radiograph reveals patchy infiltrates in both lungs suggestive of bilateral multilobar pneumonia. The patient received 2 L of normal saline with no improvement in serum creatinine. Results of testing for serum anti-GBM antibodies, ANCA, and antinuclear antibody, serum protein electrophoresis, and urine electrophoresis are pending. What is the next step in the management of this patient?

5. Renal biopsy results are as suspected. A careful inquiry into the use of nonsteroidal anti-inflammatory drugs and other drugs is negative. Serologic testing for hepatitis B and C is negative. An age-appropriate work-up for malignancy is negative. What is the next step in this patients management?